I. Field of the Invention
The invention relates to marine power steering systems and, more particularly, to a hydraulically-actuated marine power steering system providing pressurized hydraulic fluid for the system. The invention additionally relates to an improved and more versatile actuator assembly for such a system.
II. Description of Related Art
Typically, marine power steering systems for outboard motors and stern drives utilize an extendible and contractible steering ram or rod connected to the boat transom and to the propulsion unit. Extension and contraction of the piston ram in the steering link causes the propulsion unit to pivot and steer the boat. Such units require a rather large hydraulic pump since rather large volumes of hydraulic fluid are required if the steering is moved rapidly from one side to the other. Such systems also require that the engine be running in order for the steering system to operate since the hydraulic pump is powered by the engine. Two such systems are still in use today. One of the systems uses a continuous running electric powered pump which requires a high output electrical charging system to keep the system's battery charged. Most engines in the marketplace do not possess an adequate charging system which limits the use of such a system. The second system uses an electrically-powered pressure amplifier that is placed between a standard hydraulic helm and a steering cylinder on the engine. The pressure amplifier turns on and off every time a steering input is generated. The power requirement of this system is not as severe as the continuous running pump, but it is significant.
Both systems have a limited maximum volume output. In a rapid steering situation, the volume of fluid needed to steer the engine exceeds the maximum volume output of the power supply. The effect of power steering thus can be lost.
To help counter this effect, helms were designed to increase the number of steering wheel turns required to steer the engine from one side to the other. A traditional “three-turn system” requiring three steering turns to maximize the helm's steering angle now requires four or five turns. The requirement for additional turns makes it more difficult for the operator to overrun the output of the power supply. However, system responsiveness is degraded, hindering docking or other precise maneuvers.
More recently, systems have been introduced that use an accumulator to store pressurized hydraulic fluid, permitting the use of smaller pumps requiring less power. Such a system is disclosed in U.S. Pat. No. 5,241,894 (the '894 patent). The system disclosed in the '894 patent includes a pump that provides pressurized hydraulic fluid from a reservoir and a control system to selectively place the pump in an operative or inoperative mode. The hydraulic system is also provided with a valve that selectively provides pressurized hydraulic fluid to a hydraulic cylinder to cause extension or retraction of the piston ram in the cylinder. The valve is provided with ball-type check valves to control the hydraulic flow rather than using a spool-type valve which by its very nature allows for some leakage. The system can operate even when the engine is not operating, which eliminates the need for a large and continuously operating hydraulic pump.
The system disclosed in the '294 patent and later, commercial versions of that system work well, but they are designed to fit one brand of engine, namely, Mercury Marine. They are not easily usable with other brands such as Bombardier (including Eveinrude and Johnson) Honda, Yamaha, and Suzuki.
Another problem associated with the system disclosed in the '294 patent and commercial version of that system is that they require the use of relatively unreliable seals.
Thus, there remains room for improvement.